The present disclosure relates generally to air removal devices, systems and methods for liquid delivery systems. More specifically, the present disclosure relates to air removal devices, systems and methods for medical fluid delivery, such as blood, dialysis fluid, substitution fluid or intravenous drug delivery.
Due to various causes, a person's renal system can fail. Renal failure produces several physiological derangements. It is no longer possible to balance water and minerals or to excrete daily metabolic load. Toxic end products of nitrogen metabolism (urea, creatinine, uric acid, and others) can accumulate in blood and tissue.
Kidney failure and reduced kidney function have been treated with dialysis. Dialysis removes waste, toxins and excess water from the body that normal functioning kidneys would otherwise remove. Dialysis treatment for replacement of kidney functions is critical to many people because the treatment is life saving.
One type of kidney failure therapy is Hemodialysis (“HD”), which in general uses diffusion to remove waste products from a patient's blood. A diffusive gradient occurs across the semi-permeable dialyzer between the blood and an electrolyte solution called dialysate or dialysis fluid to cause diffusion.
Hemofiltration (“HF”) is an alternative renal replacement therapy that relies on a convective transport of toxins from the patient's blood. HF is accomplished by adding substitution or replacement fluid to the extracorporeal circuit during treatment (typically ten to ninety liters of such fluid). The substitution fluid and the fluid accumulated by the patient in between treatments is ultrafiltered over the course of the HF treatment, providing a convective transport mechanism that is particularly beneficial in removing middle and large molecules (in hemodialysis there is a small amount of waste removed along with the fluid gained between dialysis sessions, however, the solute drag from the removal of that ultrafiltrate is not enough to provide convective clearance).
Hemodiafiltration (“HDF”) is a treatment modality that combines convective and diffusive clearances. HDF uses dialysis fluid flowing through a dialyzer, similar to standard hemodialysis, to provide diffusive clearance. In addition, substitution solution is provided directly to the extracorporeal circuit, providing convective clearance.
Most HD (HF, HDF) treatments occur in centers. A trend towards home hemodialysis (“HHD”) exists today in part because HHD can be performed daily, offering therapeutic benefits over in-center hemodialysis treatments, which occur typically bi- or tri-weekly. Studies have shown that more frequent treatments remove more toxins and waste products than a patient receiving less frequent but perhaps longer treatments. A patient receiving more frequent treatments does not experience as much of a down cycle as does an in-center patient, who has built-up two or three days worth of toxins prior to a treatment. In certain areas, the closest dialysis center can be many miles from the patient's home causing door-to-door treatment time to consume a large portion of the day. HHD can take place overnight or during the day while the patient relaxes, works or is otherwise productive.
Another type of kidney failure therapy is peritoneal dialysis, which infuses a dialysis solution, also called dialysis fluid, into a patient's peritoneal cavity via a catheter. The dialysis fluid contacts the peritoneal membrane of the peritoneal cavity. Waste, toxins and excess water pass from the patient's bloodstream, through the peritoneal membrane and into the dialysis fluid due to diffusion and osmosis, i.e., an osmotic gradient occurs across the membrane. An osmotic agent in dialysis provides the osmotic gradient. The used or spent dialysis fluid is drained from the patient, removing waste, toxins and excess water from the patient. This cycle is repeated, e.g., multiple times.
There are various types of peritoneal dialysis therapies, including continuous ambulatory peritoneal dialysis (“CAPD”), automated peritoneal dialysis (“APD”), tidal flow dialysis and continuous flow peritoneal dialysis (“CFPD”). CAPD is a manual dialysis treatment. Here, the patient manually connects an implanted catheter to a drain to allow used or spent dialysate fluid to drain from the peritoneal cavity. The patient then connects the catheter to a bag of fresh dialysis fluid to infuse fresh dialysis fluid through the catheter and into the patient. The patient disconnects the catheter from the fresh dialysis fluid bag and allows the dialysis fluid to dwell within the peritoneal cavity, wherein the transfer of waste, toxins and excess water takes place. After a dwell period, the patient repeats the manual dialysis procedure, for example, four times per day, each treatment lasting about an hour. Manual peritoneal dialysis requires a significant amount of time and effort from the patient, leaving ample room for improvement.
Automated peritoneal dialysis (“APD”) is similar to CAPD in that the dialysis treatment includes drain, fill and dwell cycles. APD machines, however, perform the cycles automatically, typically while the patient sleeps. APD machines free patients from having to manually perform the treatment cycles and from having to transport supplies during the day. APD machines connect fluidly to an implanted catheter, to a source or bag of fresh dialysis fluid and to a fluid drain. APD machines pump fresh dialysis fluid from a dialysis fluid source, through the catheter and into the patient's peritoneal cavity. APD machines also allow for the dialysis fluid to dwell within the cavity and for the transfer of waste, toxins and excess water to take place. The source may include multiple sterile dialysis fluid solution bags.
APD machines pump used or spent dialysate from the peritoneal cavity, though the catheter, and to the drain. As with the manual process, several drain, fill and dwell cycles occur during dialysis. A “last fill” occurs at the end of APD and remains in the peritoneal cavity of the patient until the next treatment.
In any of the above modalities, entrained air and other gases are a concern. Entrained air can cause inaccuracies when pumping dialysis fluid for any of PD, HD, HF, HDF, other blood treatment modalities such continuous renal replacement therapy (“CRRT”) treatment, and intravenous drug delivery. Entrained air can cause a reduction in effective surface area in a hemodialysis filter when it accumulates on the filter fibers, leading to a reduction in effectiveness of the therapy. Entrained air entering a patient's peritoneum during PD can cause discomfort.
Regarding an extracorporeal blood therapy (e.g. HD, HF, HDF, CRRT), a gas phase may be present in the blood arising from leakage into an otherwise closed system from the outside (e.g. air sucked in via pumping), residual air not effectively primed from the device at the start of therapy, gas evolving from the blood plasma and cellular compartments (e.g. oxygen, carbon dioxide and nitrogen), and/or gas transported across a membrane from the dialysis fluid side (e.g. carbon dioxide from bicarbonate solution). While different gases may dominate in certain situations, air (78% nitrogen, 21% oxygen, 1% others) is the most typical gas. The term “air” as used herein may mean air (78% nitrogen, 21% oxygen, 1% others), while the term gas includes air and/or any other gas, e.g., carbon dioxide.
An air embolism during a blood treatment may occur when a bolus of air is infused into the patient. As little as 20 ml of air can be dangerous when introduced directly into the patient's blood system. One of the most common risks for a venous air embolism is an empty intravenous (“IV”) saline bag during rapid infusions for cramps and during a final blood rinse-back.
Microbubbles circulating in the extracorporeal circuit may present hazards when returned to patients. Microbubbles may originate in extracorporeal tubing, circulate in the blood stream until lodging in the capillary bed of various organs, mainly the lungs. During its course within the capillary, a bubble abrades the glycocalyx layer lining the surface of the vessels and thereafter obstructs blood flow through the capillary. This causes tissue ischemia, inflammatory response, and complement activation. Aggregation of platelets and clot formation may occur as well, leading to further obstruction of the microcirculation and subsequent tissue damage.
Microbubbles in the extracorporeal circuit may also contribute to platelet activation, fouling of blood-wetted surfaces with protein deposits, and flow blockages. Accumulation of bubbles in blood set recirculation zones may form foam having a high surface area, which accelerates clotting. Clots block flow through dialyzer fibers and the return fistula needle. Gas bubble induced clotting may also limit the reuse of dialyzers and blood sets.
Dialysis patients using catheter-based treatments are at the highest risk of venous air embolism since any air is introduced directly into the central blood vessels immediately. Ensuring that the catheter is clamped securely before connecting or disconnecting bloodlines limits the risk of venous air embolism. However, a venous catheter crack or disconnection may go unnoticed.
It should also be appreciated that air may be an issue for other treatments requiring the delivery of a fluid to a patient, such as PD and intravenous drug delivery.
For each of the above reasons and scenarios, a need exists to provide an apparatus that ensures that entrained air is removed from blood, dialysis fluid, substitution fluid or an intravenous drug during treatment and prior to delivering or returning such fluids to the patient.